Field of Invention
The present invention belongs to the field of semiconductor illumination and in particular relates to a GaN-based LED epitaxial structure and a preparation method thereof.
Description of Related Arts
Due to the advantages of long service life, low energy consumption and the like, LED (Light Emitting Diode) has been widely applied to various fields. Especially with the increasing great improvement of the illumination performance index thereof, LED is usually used as a light emitting device in the field of illumination. III-V family compound semiconductors represented by gallium nitride (GaN), especially InGaN/GaN-based (indium gallium nitride/gallium nitride) LEDs have a huge application potential in the field of photoelectronic devices such as high-brightness blue light emitting diodes and blue light lasers due to the features such as wide band gap, high luminous efficiency, high electron saturation drift velocity and stable chemical property, and are widely concerned by people.
However, since an InGaN/GaN structure has the problem of very great lattice and thermal expansion coefficient mismatches, consequently a polarized electric field exists in a quantum well. This polarized electric field easily causes the quantum well to be inclined. As a result, electron and hole wave functions in the quantum well are spatially separated and thereby recombination efficiency of electrons and holes is decreased. Although the luminous efficiency of the current InGaN/GaN LEDs has already been obviously improved, for high-power GaN-based LEDs, the problem of serious quantum efficiency droop still exists and the inner quantum efficiency of the LEDs is quickly drooped even under the situation of large current injection. In addition, leakage of electrons towards a P end is one of reasons which cause low efficiency.
The above-mentioned problems are mainly caused by the existence of the polarized electric field in a well due to the lattice mismatch of the InGaN/GaN quantum well structure, the existence of the polarized electric field causes electron and hole wave functions in the quantum well to be spatially separated and thereby the recombination efficiency of electrons and holes is decreased. Therefore, in order to decrease the negative effect of the built-in polarized electric field, the prior art usually adopts InGaN, ALINGAN and the like to decrease the mismatch between potential barriers and potential wells; and there are people who put forward a method of realizing lattice mismatch decrease by gradually changing indium components in the potential wells. However, since indium atoms are easily volatilized from epitaxial materials under the condition of heating, it is very difficult to realize the above-mentioned methods according to set values.
In view of the above-mentioned defects of the prior art, it is really necessary to provide a GaN-based LED epitaxial structure and a preparation method which have the advantages that the distribution of electrons in each luminous well can be enabled to be more uniform, the leakage of the electrons towards the P end can be reduced and thus the luminous efficiency of the quantum well can be improved.